This disclosure relates generally to a semiconductor chip package, and more specifically to a rectangular-shaped controlled collapse chip connection (C4) used to connect a semiconductor chip package substrate and a semiconductor chip.
A semiconductor chip also commonly referred to as an integrated circuit or a die is typically assembled into a semiconductor chip package that is soldered to a printed circuit board. One type of semiconductor chip package is a flip chip, also known as a C4 package. The semiconductor chip package typically includes the semiconductor chip which contains a number of round solder bumps that are attached to a top surface of the chip. The semiconductor chip via the solder bumps is soldered to pads located along a top surface of a semiconductor chip package substrate forming a metallurgical joint between the chip and the substrate. The substrate is typically constructed from a composite material which has a coefficient of thermal expansion (CTE) that is different than the CTE for the semiconductor chip. In particular, the CTE of the semiconductor chip is relatively low (e.g., 2-3 parts per million) compared to the CTE of the substrate (e.g., 17-20 parts per million). As a result, the semiconductor chip expands relatively slow in comparison to the substrate, which expands relatively fast. Any variation in the temperature of the package may cause a resultant differential expansion between the semiconductor chip and the substrate. As a result, the surfaces of the semiconductor chip and the substrate lose proximity with respect to each other. Consequently, the differential expansion may induce stresses that can crack the round solder bumps. The solder bumps carry electrical current between the semiconductor chip and the substrate, so any crack in the bumps may affect the operation of the chip.